U.S. patent number 4,707,990 [Application Number 07/019,651] was granted by the patent office on 1987-11-24 for solar powered stirling engine.
This patent grant is currently assigned to Stirling Thermal Motors, Inc.. Invention is credited to Roelf J. Meijer.
United States Patent |
4,707,990 |
Meijer |
November 24, 1987 |
Solar powered Stirling engine
Abstract
The effectiveness of the lubrication system of a Stirling engine
is maintained in a solar dish module for all directions of aiming
of the dish by the journal mounting of the engine on the dish
module with the center of gravity of the journaled mass eccentric
to the journal axis along a particular radial. The engine has a
sump which is disposed at a low point of the engine. The center of
gravity of the journaled mass lies along a radial from the journal
axis which intersects the sump. An additional counterweight is
added to achieve the desired eccentricity.
Inventors: |
Meijer; Roelf J. (Ann Arbor,
MI) |
Assignee: |
Stirling Thermal Motors, Inc.
(Ann Arbor, MI)
|
Family
ID: |
21794318 |
Appl.
No.: |
07/019,651 |
Filed: |
February 27, 1987 |
Current U.S.
Class: |
60/641.15;
60/641.8 |
Current CPC
Class: |
F24S
23/71 (20180501); F02G 1/055 (20130101); F03G
6/068 (20130101); F24S 30/458 (20180501); F24S
20/20 (20180501); F02G 2255/00 (20130101); F02G
2254/30 (20130101); Y02E 10/47 (20130101); Y02E
10/40 (20130101); F24S 25/10 (20180501); F24S
2030/18 (20180501); Y02E 10/46 (20130101) |
Current International
Class: |
F24J
2/54 (20060101); F24J 2/00 (20060101); F24J
2/06 (20060101); F02G 1/055 (20060101); F02G
1/00 (20060101); F03G 6/06 (20060101); F03G
6/00 (20060101); F24J 2/12 (20060101); F03G
007/02 () |
Field of
Search: |
;60/641.8,641.15 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Ostrager; Allen M.
Attorney, Agent or Firm: Harness, Dickey & Pierce
Claims
What is claimed is:
1. In a solar dish module which comprises a dish which receives
incident solar rays and reflects them to a focus at which is
located the combination of a receiver and a heat engine organized
and arranged so that the heat energy of the reflected solar rays
collected at the receiver powers the engine, and wherein the
receiver and heat engine are supported from the dish by a
framework, the improvement which comprises journal means for
journaling at least the engine on the framework to maintain certain
predetermined spatial orientation for the engine in relation to the
direction of gravity irrespective of spatial orientation of the
dish.
2. The improvement set forth in claim 1 in which the certain
predetermined spatial orientation for the engine is maintained by
having the journal axis in the same direction as the dish axis.
3. The improvement set forth in claim 2 in which the journal means
comprises a pair of main bearings axially spaced apart.
4. The improvement set forth in claim 3 in which the collector is
attached to the engine so as to be journaled via the engine on the
framework.
5. The improvement set forth in claim 4 wherein said collector has
a longitudinal axis located below said journal axis.
6. The improvement set forth in claim 1 in which the engine has a
lubrication system including a sump and the center of gravity of
the total mass journaled by the journal means is effective to
maintain the sump intersected by a vertical plane which passes
through the journal axis.
7. The improvement set forth in claim 6 including a counterweight
supported from the engine to cause the center of gravity of the
total journaled mass to be so effective.
8. The improvement set forth in claim 1 wherein the engine has a
journal axis and a lubrication system including a sump and wherein
said predetermined spatial orientation is one in which said sump is
below said engine and said receiver is also positioned so that its
center of gravity is below the journal axis of said engine.
9. The improvement set forth in claim 8 further including a
counterweight secured to said engine and positioned below the
center of gravity of the total mass journaled on said axis.
Description
This invention relates to a solar powered engine and specifically
to a new and unique arrangement for mounting a hot gas engine, such
as a Stirling cycle engine, in association with a solar dish
collector.
It has heretofore been proposed to generate electricity from solar
power by utilizing the overall combination of a solar dish
collector, a hot gas engine, and an electric generator. In general
the dish is aimed at the sun to reflect incident sunlight onto the
receiver which is located at the dish's focus. The heat energy so
collected is utilized to drive a hot gas engine such as a Stirling
engine, which is mounted adjacent the receiver. The engine in turn
drives the generator to create electric power.
Preferably the combination of receiver, engine and generator is
organized and arranged to cast as small a shadow as possible on the
dish. Hence it is desirable for the receiver, engine and generator
to be generally coaxially arranged along the axis of the dish. They
are supported at a spaced distance from the dish by a framework
which extends back to the dish.
In order to efficiently operate a solar powered system which has a
dish, it is important that the dish be continuously aimed in the
direction of incident sunlight. Hence dishes typically comprise
tracking systems which develop the correct combination of azimuth
and elevation motions to keep the dish pointed at the sun. During
the course of a solar tracking day, from early morning to late
afternoon, the dish tracks the sun along an arc which has
continuously increasing azimuth. The elevation begins at or near
the horizon in the east, and increases until midday. Thereafter the
elevation decreases toward the western horizon.
Depending upon time of year and latitude at which it is located,
any given solar dish module may track an arc which spans a
significant range of azimuth and elevation motions. Indeed the
amount of azimuthal motion in the course of a day of solar tracking
may span an arc considerably more than 180 degrees, and in fact a
dish module may have a full 360 degrees azimuthal rotational range.
Likewise a full elevational range of motion will extend from
horizon to zenith.
The exact manner in which the composite dish motion (meaning
combination of azimuth and elevation motions) is generated depends
on the dish module mechanism. Different modules are constructed
with different mechanisms for creating the desired composite
motion. Regardless of the module mechanism, mounting of a
receiver-engine-generator combination on a dish module in the
general manner described above results in the axis of the
combination being aimed in the same direction as the dish is
pointed.
The present invention arises through recognition that mounting of
what would be considered as a standard engine on at least certain
kinds of dish modules will subject the engine to spatial
orientations which are significant departures from what would be
considered normal spatial orientations. For example, a standard
engine is designed with the intent that it will be used generally
upright and with its axis generally horizontal. When mounted on a
dish module, however, such an engine will experience departures
from this intent. Depending upon the particular dish mechanism,
these departures can be considered analogous to roll, and/or pitch,
and/or yaw. Engine designs can usually tolerate certain degrees of
departure in these components of spatial displacement; however,
there are limits and therefore, engine considerations impose
restrictions on the range of motion for at least certain kinds of
dish modules.
One especially critical aspect of engine operation involves the
lubrication system. The usual engine requires lubrication of its
moving internal parts, and therefore has an internal lubrication
system for delivering lubricant to them. Generally a pump draws
lubricant from a sump and delivers it to the points requiring
lubrication, with the lubricant subsequently returning to the sump.
By its nature, this type of lubrication system depends on gravity
and therefore is sensitive to the spatial orientation of the
engine. For example, if the engine is tipped too much so that it is
no longer within its range of uprightness, the lubrication system
becomes ineffective because lubricant cannot be drawn from nor
returned to the sump.
Fixed mounting of a Stirling engine on certain types of dish
modules therefore inherently imposes restrictions on dish aiming
and may consequently limit the range of solar tracking. If the
engine is tipped beyond the ability of the lubrication system to
deliver ample lubricant to moving parts, the engine may fail.
The present invention is directed to an improvement in the basic
dish-receiver-engine combination described above which enables a
conventional engine to be utilized effectively without modification
to the engine mechanism, particularly its internal workings and
lubrication system, in solar dish modules where the engine would
otherwise be subjected to tipping beyond its range of
uprightness.
The present invention in a preferred embodiment comprises mounting
at least the engine on the dish module so that predetermined
spatial orientation of the engine is maintained throughout the
range of pointing of the dish. In the disclosed embodiment this is
done by journaling the engine on an axis which is either coaxial or
parallel with the axis of the dish. By journaling the engine such
that its center of gravity is eccentric to the journal axis, along
a particular radial to the dish axis, the engine maintains a
particular uprightness irrespective of the direction in which the
dish is pointed such that the engine's lubrication system remains
effective. In other words the pump stays in communication with the
supply of lubricant in the sump so that lubricant continues to be
delivered to moving parts, and returns to the sump.
The receiver axis is preferably arranged coaxial with the dish so
that maximum solar energy collection is assured. Generally the
receiver will be attached to the engine so that journaling of the
engine on the dish inherently journals the receiver as well. With
the receiver coaxial with the dish and the receiver surface
essentially symmetrical about the receiver axis, the journaling of
the receiver with the engine does not impair its efficiency.
However, the preference for coaxially arranging the receiver with
the dish in conjunction with the particular engine and receiver and
their attachment to each other may result in the engine's center of
gravity being other than along the radial which will yield the
preferred uprightness. Consequently, a counterweight of appropriate
mass is associated with the receiver-engine combination at an
appropriate location such that the proper center of gravity of the
combination is achieved for causing the combination to continuously
assume the preferred uprightness which enables lubricant to be
delivered to the engine's moving parts for all directions of dish
pointing.
Since existing dish modules already comprise a framework for
supporting the receiver-engine-generator combination on the dish,
the only change which is necessitated with incorporation of the
present invention is inclusion of a journal mounting of the
combination on the framework and possibly a counterweight.
Journaling can be accomplished with conventional components
including, for example, ball and/or roller bearing assemblies. The
counterweight, if required, can be nothing more than a mass of any
dense inexpensive material suitably mounted on the engine-receiver
combination.
The invention is described with reference to the accompanying
drawings which portray a preferred embodiment according to the best
mode presently contemplated.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an elevational view of the dish receiver and Stirling
engine combination of the present invention and illustrating the
directional and seasonal orientation of the receiver.
FIG. 2 is an enlarged fragmentary longitudinal sectional view of
the engine-receiver structure.
FIG. 3 is a fragmentary view, partly in section and on an enlarged
scale, in the same direction as the view of FIG. 2 illustrating
more detail.
FIG. 4 is a side view of the receiver which forms a part of the
structure shown in FIG. 2 and only a fragment of which is shown in
FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 shows a dish collector module 4 comprising a parabolic
reflecting dish 6 which is supported for azimuthal and elevational
motions. The dish 6 is supported on the outer end of an arm 8 that
is pivotally supported at its inner end on a bracket 10 for up and
down movement about an axis D. Arm 8 can be inclined from the
vertical 12 angularly about the horizontal axis D passing through
the arm and the bracket 10. The bracket 10 is rotatably supported
on upwardly inclined leg 12 of fixed support 14 so that the dish
module 4 can be rotated about axis T.
Appropriate motive means are used to impart rotational motion to
the dish about axis T and to the arm 8 about axis D and there are
suitable controls associated with the motive means for causing the
dish to track the sun as it travels across the sky. Such motive
means and controls are conventional and will not be explained in
further detail here. Suffice it to say that the controls operate to
keep the dish axis 19 pointed at the sun, parallel with the
direction of incident sunlight.
The dish 6 serves to concentrate the solar rays which are incident
upon it by reflecting them to the focal point at which a solar
receiver 20 is located. Mounted in association with receiver 20 are
a Stirling engine 22 and an electric generator 24. The combination
of receiver, Stirling engine, and generator is supported by
suitable structural framework 26. Further details of the receiver
20, engine 22 and generator 24 are illustrated in FIGS. 2-4.
Receiver 20 (FIG. 4) is of cylindrical tapering shape. It is
disposed coaxial with dish axis 19, and comprises an aperture 28
which is open toward the dish. Aperture 28 is coaxial with axis 19
and has a frustoconical shape and a size to expose essentially the
entire of the interior receiver surface of the receiver 20 to the
reflected solar rays. Particular details of the receiver are not
important insofar as general principles of the present invention
are concerned since the receiver is essentially conventional. It
comprises any suitable construction which is effective to absorb
the solar energy and transfer the heat to engine 22. For example,
one means of doing this is by a suitable medium which is heated in
the receiver, circulated to the engine where it gives up heat to
the engine, and then is recirculated back to the receiver for
reheating.
The end of receiver 20 opposite aperture 28 is attached to the
housing 32 of engine 22, and any suitable form of connection may be
employed. Particular details will depend upon the specific engine
and receiver involved. The joining of the receiver to the engine
can be advantageous for this embodiment of the invention if the
receiver makes a positive contribution to the preferred uprightness
of the engine. The axis of the engine output is identified by the
reference numeral 34 and it can be seen in FIG. 2 that this axis 34
is eccentric relative to axis 19. Engine 22 may be any suitable
type, and an exemplary type of engine is depicted in U.S. Pat. No.
4,481,771, commonly assigned.
Electric generator 24 has a frame 35 which is attached to engine
housing 32 by any suitable means of attachment. Referring to FIG.
3, generator 24 comprises a rotor 36 and a stator 38. Rotation of
rotor 36 is effective to generate electric voltage in stator 38
which in turn can be delivered to any desired means of utilization
which requires electric power. Details of the generator are
conventional and therefore will not be described. It is sufficient
to note that rotor 36 is journaled in bearings 40 on the generator
frame. Engine 22 has an output shaft 42 along axis 34 connected to
drive rotor 36, ths axis of the generator being coaxial with axis
34.
FIG. 2 also portrays a fan 46 at the end of generator 24 opposite
engine 22. The fan may be connected to the rotor so that the
engine, in addition to driving the rotor, also drives the fan. In
this way fan 46 will be effective to draw cooling air across the
electric generator's frame.
The receiver-engine-generator combination is journaled on framework
26 about the axis 34. The two points of journaling are at main
bearings 50 and 52.
The main bearing 52 comprises a bearing plate 54 arranged
perpendicular to axis 34 and containing a large roller bearing
assembly 52 which journals the circular wall of the engine
housing.
The main bearing 50 includes a bearing plate 58 which journals a
shaft 62. This shaft 62 is a part of a sub-frame 64 which is
attached to generator frame 35. The two main bearing plates 54, 58
are supported from a beam 66 which is parallel to the journal axis
so that the parts 54, 58, 66 cooperatively form what may be
considered as an inverted cradle.
Assuming that axes 19 and 34 are horizontal, FIG. 2 portrays the
usual spatial orientation of the engine with the engine being
upright. In this orientation, the oil sump 70 associated with the
engine is disposed at essentially the lowest point of the engine.
The engine will continue to operate properly so long as this
relationship is maintained because the internal lubrication pump
(not visible) will be able to draw lubricant from the sump and
deliver it to the moving internal parts, and the lubricant will
then return to the sump. However, beyond certain deviations from
this relationship, the lubrication system will no longer be
effective to draw oil out of the sump, and consequently the engine
will be prone to failure due to loss of lubrication. The particular
amount of deviation beyond which the lubrication system becomes
ineffective is to a certain extent a function of the particular
engine design.
According to the present invention, the center of gravity of the
journaled mass is arranged eccentric to the journal axis such that
the sump is consistently maintained vertically below the engine
axis 34, in the manner portrayed in FIG. 2, regardless of the
direction in which the dish is aimed. The engine axis 34 does
experience tipping but that tipping is due to the angular
elevational component of dish axis 19.
By having the center of gravity of the journaled mass lie between
axis 34 and sump 70, the engine-receiver-generator combination will
assume a single unique circumferential orientation about the
journal axis to thereby define a preferred uprightness for the
engine. This unique orientation serves to maintain the sump 70 at
essentially the lowest point of the engine regardless of direction
in which the dish is pointed.
One way to achieve proper center of gravity is by attaching
counterweight 72 to the engine directly below sump 70 as shown in
FIG. 2. The mass of the counterweight is sufficient in relation to
the distance from the journal axis that a sufficient torque is
produced to overcome the inertia and friction of the journaled mass
so that as the inverted cradle of parts 54, 58, 66 is angularly
positioned about the journal axis over a range of positions due to
solar tracking of the dish, the journaled mass maintains sump 70 in
a vertical plane which is radial to axis 19. For any given
engine-receiver-generator combination, the center of gravity may be
other than the one just described. Therefore use of a counterweight
to achieve the desired placement for the center of gravity will in
all likelihood be needed.
While tipping of the engine will occur as dish axis 19 is
increasingly elevated, the sump will nonetheless remain at the
lowest point of the engine so that a sufficient lubrication
delivery is assured.
In the absence of the journal feature of the present invention, a
fixed mounting of the engine on the illustrated dish would result
in the sump being, at times, other than directly vertically below
the engine where it could possibly experience lubrication system
failure on account of the gravity-sensitive nature of the system.
With the present invention that possibility is eliminated.
Although the illustrated embodiment comprises the use of a separate
counterweight, it will be appreciated that other embodiments may
have the particular constructions and arrangements of the
engine-receiver-generator such that they inherently produce the
proper counterweighting without additional weight. Likewise in
certain applications of the invention, journaling of the engine
alone and/or in combination with only one of either the receiver
and generator may be satisfactory. Also forms of loads other than
an electric generator could conceivably be driven by the engine
although it is expected that electric power generator will be the
most common usage for solar powered dish modules.
* * * * *